This invention relates to optical imaging of submicron surface features by use of a microscope objective employing total internal reflection modified by partial coupling of radiant energy to the subject surface via an evanescent mode of energy propagation to obtain variations in received signal levels corresponding to variations in surface height, the signal amplitudes being presented as a y-axis deflection upon an x-y display wherein each of a plurality of x scan lines represent a strip of the subject surface to form the likeness of a three dimensional view of the surface.
There is a need to measure very fine surface details in a variety of disciplines ranging from the production of magnetic recording media to the biological examination of living cells, by way of example. In the case of the magnetic media, variations in surface height or deviations from planarity are of interest, while in studies of a cell from biological subject matter, differences in the density of the biological material of the cell are of interest. One technique for viewing minute details at the subject surface or within a shallow region beneath the surface, within a fraction of the optical wavelength, employs a microscope objective placed within approximately one wavelength of the subject in conjunction with inclined rays of illuminating light to provide internal reflection within the objective as is disclosed in Guerra et al., U.S. Pat. No. 4,681,451. Since photons are able to propagate across the gap between the lens and the subject, this form of microscopy is often referred to as photon tunneling microscopy. Such microscopy is described also in an article Photon Tunneling Microscopy by J. M. Guerra in APPLIED OPTICS, Sep. 10, 1990, pages 3741-3752. Therein, the subject is spaced apart from the objective lens at a spacing which is so small that a fraction of the optical energy is coupled to the subject via evanescent mode propagation resulting in a partial frustration of the total internal reflection at the lens. There results a variation in intensity of received optical signal, the variation in intensity being representative of variations in spacing between the subject and the lens.
While the apparatus and methodology of the foregoing patent are successful in obtaining surface data, there is a need for a mode of data presentation which enables a viewer of the subject matter to visualize better the topography of the subject surface as well as details in a shallow region below the surface. An improved mode of data presentation would allow the viewer to recognize patterns representative of surface undulations and/or variations in the density or optical characteristics of the subject. Such patterns, if presented with a likeness of a three-dimensional presentation would be most useful to an engineer, in the case of the magnetic medium, for evaluating the suitability of the magnetic media for recording apparatus, or for a pathologist, in the case of the biological cell, for diagnosing an ailment.